"It's never easy to lose such a vital, irreplaceable member of the family, but this is downright heartbreaking," Hamill wrote. "Carrie was one-of-a-kind who belonged to us all – whether she liked it or not. She was our Princess, damn it, and the actress who played her blurred into one gorgeous, fiercely independent and ferociously funny, take-charge woman who took our collective breath away. Determined and tough, but with a vulnerability that made you root for her and want her to succeed and be happy."
Hamill and Fisher famously portrayed Luke and Leia Skywalker in the Star Wars movies. After appearing in the original trilogy, the two returned for 2015's The Force Awakens and were slated to appear in Episode VIII and Episode IX.
In his Facebook post, Hamill reflected on his long relationship with Fisher, writing, "She played such a crucial role in my professional and personal life, and both would have been far emptier without her. I am grateful for the laughter, the wisdom, the kindness and even the bratty, self-indulgent crap my beloved space-twin gave me through the years."
Hamill's Facebook post followed a brief but poignant message he posted earlier on Twitter: "No words #Devastated," alongside a picture of himself and Fisher in-costume as Luke and Leia.
Other members of the extended Star Wars family have also shared tributes to Fisher, including Harrison Ford, Billy Dee Williams, Force Awakens director J.J. Abrams and franchise creator George Lucas. Fisher died after suffering a massive heart attack while onboard a flight traveling from London to Los Angeles last Friday.